Performance simulation of 3G closed loop transmit diversity systems

It is well known that the third generation partnership project (3GPP) for WCDMA FDD has chosen Space Time Transmit Diversity (STTD) (known also as open loop transmit diversity) and Feedback Mode Transmit Diversity (FBTD) (known also as closed loop transmit diversity) as transmit diversity techniques for two transmit antennas. In this paper, we look into the performance of closed loop transmit diversity schemes in the downlink of a WCDMA systems release 4. More specifically, we compare by simulations in a very realistic environment the mode 1 and mode 2 performance of the FBTD scheme. The resulting simulation curves show (i) the effect of varying mobile speeds on the performance of the two modes of FBTD with and without fast closed loop power control, (ii) the impact of channel estimation errors on the average bit error rate (BER), and (iii) the consequences of errors in the feedback path between receiver and transmitter.